LeetCode之21. Merge Two Sorted Lists

1. 方法1 (递归)

1.1 C# 代码

/**
* Definition for singly-linked list.
* public class ListNode {
*     public int val;
*     public ListNode next;
*     public ListNode(int x) { val = x; }
* }
*/
public class Solution {
public ListNode MergeTwoLists(ListNode l1, ListNode l2) {

if(l1 == null)
return l2;
if(l2 == null)
return l1;
if(l1.val > l2.val)
{
ListNode tmp = l2;
tmp.next = MergeTwoLists(l1, l2.next);
return tmp;
}
else
{
ListNode tmp = l1;
tmp.next = MergeTwoLists(l1.next, l2);
return tmp;
}
}
}

1.2 Python3 代码

2. 方法2（迭代）

2.1 C# 代码

/**
* Definition for singly-linked list.
* public class ListNode {
*     public int val;
*     public ListNode next;
*     public ListNode(int x) { val = x; }
* }
*/
public class Solution {
public ListNode MergeTwoLists(ListNode l1, ListNode l2) {

if(l1 == null) return l2;
if(l2 == null) return l1;
ListNode result = new ListNode(0);
ListNode Hc = result;
while(l1 != null && l2 != null)
{
if(l1.val < l2.val)
{
Hc.next = l1;
l1 = l1.next;
}
else
{
Hc.next = l2;
l2 = l2.next;
}
Hc = Hc.next;
}

if(l1 != null)
{
l2 = l1;
}

while(l2 != null)
{
Hc.next = l2;
Hc = Hc.next;
l2 = l2.next;
}

return result.next;
}
}

2.2 Python 3代码